Identification of mutations in receptor and non-receptor protein kinases that drive malignant transformation of cancer cells ('driver' mutations) have revolutionized patient care by opening the door to patient-tailored targeted therapies that can improve patient survival. In order to discover new targets for therapy, we sequenced the coding regions of -100 melanomas and identified a large number of somatic mutations and inherited Single Nucleotide Variants (SNVs). One of the most important findings of this effort is the identification ofthe RAC1 signaling pathway as a potential new target for melanoma therapy. The analysis revealed a recurrent, UV signature activating mutation in this RHO family of small GTPases, RAC[P29S], in ~5% of melanomas, in addition, the sequencing data revealed mutations in upstream regulators and downstream effectors of RAC1 pathway in a large numbers of melanoma tumors. Functional studies demonstrated an important role in proliferation and migration of not only mutant but also melanoma cells that that donot harbor the P29S mutation. The data suggest that pharmacological inhibition of RACl or its critical effeGtor(s) can be applied for development of new therapies for melanoma patients. The general goals ofthis project are to determine the frequency and prognostic significance of RAC[P29S] mutation in sun exposed melanocytic lesions, and to identify downstream effectors of RACl most likely to be druggable targets in this pathway. The specific aims are: Aim 1: To determine the frequency of RAC1[P29S] mutation and RACl expression levels in a large cohort of melanocytic lesions and correlate with pathological features and tumor progression; Aim 2: To elucidate the downstream targets of activated RACl in melanomas. Aim 3: To identify small-molecule inhibitors of PAK kinases, the RACl effectors. These studies are likely to provide new opportunities for drug discovery for melanomas and possibly other cancers that can facilitate patienttailored targeted therapy.